JP7381867B2 - Terahertz light generation device and terahertz light generation method - Google Patents

Description

The present invention relates to a terahertz light generation device and a terahertz light generation method, and more particularly, to a terahertz light generation device and a terahertz light generation method, and more specifically, a terahertz light generation device that generates terahertz light by making pump light and seed light enter a nonlinear optical crystal at an intersection angle that satisfies a predetermined phase matching condition. The present invention relates to a generator and a terahertz light generation method for measuring the intersection angle between pump light and seed light.

Conventionally, terahertz light generation devices are known, and for example, as an optical injection type terahertz parametric generator (Is-TPG), there are a pump light oscillator that oscillates pump light, a seed light oscillator that oscillates seed light, and a pump light oscillator that oscillates seed light. A device is known that includes a nonlinear optical crystal that generates terahertz light when light is incident at an intersection angle that satisfies a required phase matching condition (Patent Document 1).
In particular, the terahertz light generating device of Patent Document 1 is capable of generating terahertz light of a required wavelength, and the pump light and seed light are directed to the nonlinear optical crystal at an intersection angle that satisfies the required phase matching condition. A light guide means is provided for guiding at least one of the pump light and the seed light so as to be incident thereon.

JP2018-77427A

In Patent Document 1, the intersection angle between the pump light and the seed light can be set using the light guiding means, but in reality, there are mechanical errors in the entire device, so the light guiding means is used to set the intersection angle between the pump light and the seed light. It is necessary to check whether the intersection angle between the emitted pump light and the seed light satisfies the phase matching condition.
To do this, we removed the nonlinear optical crystal from the terahertz light generator, measured the distance between the optical axes of the pump light and the seed light at two points separated from the intersection of the pump light and the seed light, and A method has been adopted in which the intersection angle is calculated using the distance between the optical axes of the two points and the distance from the intersection position to each measurement position.
However, such a measurement method requires operations such as removing and attaching the nonlinear optical crystal, and there is a problem that the operations are complicated, and there is a risk that further deviations may occur due to these operations.
In view of these problems, the present invention provides a terahertz light generation device that can easily measure the intersection angle between pump light and seed light, and also provides a terahertz light generation method.

That is, the terahertz light generation device according to the invention of claim 1 includes a pump light oscillator that oscillates pump light, a seed light oscillator that oscillates seed light, and the pump light and the seed light satisfy a required phase matching condition. a nonlinear optical crystal that generates terahertz light when incident at an intersecting angle; and a nonlinear optical crystal that generates terahertz light when incident at an intersecting angle ; A terahertz light generation device comprising a light guiding means for guiding at least one of the lights ,
an extraction means provided between the light guiding means and the nonlinear optical crystal , for taking out a part of the pump light and the seed light and irradiating the rest onto the nonlinear optical crystal; and a pump taken out from the extraction means. an intersection position defining member provided at an intersection position of the light and the seed light , and having a passage section formed therein for passing the pump light and the seed light ; an imaging means for receiving light, an optical axis distance measuring means for measuring an optical axis distance between the pump light and the seed light based on an image received by the imaging means, and a distance between the optical axes and the imaging means. The present invention is characterized by comprising a calculation means for calculating an intersection angle between the pump light and the seed light from the distance between the members to the intersection position defining member.
Further, the terahertz light generation method according to the invention of claim 4 includes a pump light oscillator that oscillates pump light, a seed light oscillator that oscillates seed light, and the pump light and the seed light satisfy a required phase matching condition. a nonlinear optical crystal that generates terahertz light when incident at an intersecting angle; and a nonlinear optical crystal that generates terahertz light when incident at an intersecting angle ; For a terahertz light generation device equipped with a light guiding means for guiding at least one of the lights ,
Taking out a part of the pump light and the seed light before entering the nonlinear optical crystal,
disposing an intersection position defining member having a passage portion through which the pump light and the seed light can pass, at an intersection position where the extracted pump light and the seed light intersect;
receiving the pump light and the seed light that have passed through the passage portion of the intersection position defining member by an imaging means;
The distance between the pump light and the seed light is determined from the distance between the optical axes of the pump light and the seed light recognized from the image taken by the imaging means and the distance between the members from the imaging means to the intersection position defining member. It is characterized by calculating the intersection angle.

According to the above invention, since a part of the pump light and seed light is taken out to measure the intersection angle, the work can be carried out with the nonlinear optical crystal attached, and there is no shift due to replacement, so it is efficient. Moreover, the intersection angle can be easily measured.

A plan view of the terahertz light generation device according to this example Enlarged view of the intersection angle measurement device that measures the intersection angle of the pump light and seed light Reference images of pump light and seed light taken by imaging means

The illustrated embodiment will be described below. FIG. 1 shows a terahertz light generating apparatus 1 that performs a quality inspection of an object to be inspected O using terahertz light TH.
The terahertz light generating device 1 includes a pump light oscillator 2 that oscillates pump light L1, a seed light oscillator 3 that oscillates seed light L2, and generates terahertz light TH when the seed light L2 and pump light L1 are incident. a nonlinear optical crystal 4, and a light guiding means 5 for making the seed light L2 oscillated from the seed light oscillator 3 incident on the nonlinear optical crystal 4 at a predetermined angle of incidence, and these are connected to a personal computer (PC) or the like. It is controlled by a control means 6 consisting of a programmable logic computer (PLC).
According to the terahertz light generation device 1 having the above configuration, the terahertz light TH is generated by making the seed light L2 and the pump light L1 enter the nonlinear optical crystal 4 at a required intersection angle θ that satisfies the phase matching condition. The terahertz light generator 1 of this embodiment is configured as a light injection type terahertz parametric generator (Is-TPG).

The pump light oscillator 2 is composed of a microchip laser that emits laser light as the pump light L1, and is supported horizontally at the same height as the nonlinear optical crystal 4 at a position apart from the end surface 4A of the nonlinear optical crystal 4. .
The pump light L1 oscillated by the pump light oscillator 2 is incident perpendicularly to the center of the end surface 4A of the nonlinear optical crystal 4 (the position where the axis of the nonlinear optical crystal 4 intersects the end surface 4A). There is.
Further, a damper 7 is provided on the optical axis of the pump light L1 to absorb the pump light L1 that has passed through the nonlinear optical crystal 4 and the idler light L3 generated within the nonlinear optical crystal 4.
Further, a collimator 8 is disposed between the pump light oscillator 2 and the nonlinear optical crystal 4, and the pump light L1 is adjusted into a parallel beam by the collimator 8, and then enters the end surface 4A of the nonlinear optical crystal 4. It looks like this.
The pump light oscillator 2 pulses the laser light as the pump light L1 toward the nonlinear optical crystal 4. In this embodiment, the wavelength of the pulsed laser is 1064.4 nm, and the repetition frequency during pulse oscillation is 100 Hz. , the pulse width is 400 psec.

The seed light oscillator 3 is composed of a semiconductor laser that emits laser light as the seed light L2, and is fixed horizontally in parallel to the axis of the nonlinear optical crystal 4 and at the same height as the nonlinear optical crystal 4. ing.
The seed light oscillator 3 is configured to continuously oscillate the seed light L2, and although the optical path of the seed light L2 immediately after oscillation is parallel to the axis of the nonlinear optical crystal 4, the oscillation direction is parallel to the pump axis. The direction is set opposite to the oscillation direction of the pump light L1 oscillated from the optical oscillator 2.
In this embodiment, the wavelength of the laser beam as the seed light L2 is variable in the range of 1068 to 1075 nm, so that the nonlinear optical crystal 4 generates terahertz light TH of 0.8 to 3 THz. It is now possible.

The nonlinear optical crystal 4 is formed into a quadrangular column shape, and its axis is provided horizontally at a predetermined height. The seed light L2 is made to cross and enter.
When the intersection angle θ between the pump light L1 and the seed light L2 incident on the end surface 4A of the nonlinear optical crystal 4 satisfies the phase matching condition, terahertz light TH is generated in the nonlinear optical crystal 4. There is.
Further, when the intersection position of the pump light L1 and the seed light L2 is located at the end surface 4A of the nonlinear optical crystal 4, it is possible to generate the terahertz light TH with high efficiency.
In this embodiment, in order to position the intersection position of the pump light L1 and the seed light L2 at the end surface 4A during maintenance of the terahertz light generator 1, the nonlinear optical crystal 4 is connected to the pump light L1. A crystal moving means 14 is provided for moving the crystal along the optical axis direction.

A silicon prism 11 is integrally attached to the side surface of the nonlinear optical crystal 4, and the terahertz light TH is radiated outward through the silicon prism 11.
In addition, a pair of convex lenses 12A and 12B are arranged spaced apart on the optical path of the terahertz light TH emitted from the silicon prism 11, and a pair of convex lenses 12A and 12B are arranged at a distance from each other on the optical path of the terahertz light TH emitted from the silicon prism 11. A light receiving element 13 to be used is arranged.
With such a configuration, when inspecting the inspection object O, the inspection object O is set at an intermediate position between the pair of convex lenses 12A and 12B, and the terahertz light TH after passing through the inspection object O is By causing the light receiving element 13 to receive light, the quality of the inspection object O is determined.

The light guide means 5 guides the seed light L2 oscillated from the seed light oscillator 3 to the nonlinear optical crystal 4, and is located on the side of the seed light oscillator 3 (with respect to the optical axis of the pump light L1). A first total reflection mirror 21 provided on the opposite side (lower part in the figure) with respect to the optical axis of the pump light L1; It is composed of a convex lens 23 provided between a reflecting mirror 22 and a convex lens 23.
Further, a collimator 24 is provided between the seed light oscillator 3 and the first total reflection mirror 21 on the optical path of the seed light L2, and the collimator 24 passes the seed light L2 immediately after being oscillated from the seed light oscillator 3. It is designed to adjust so that the light beams are parallel.
The first total reflection mirror 21 is supported at an angle of 45 degrees with respect to the optical axis of the seed light L2 emitted from the seed light oscillator 3, thereby directing the seed light L2 toward the convex lens 23. It is designed to reflect at a 90° angle.
Further, the first total reflection mirror 21 of this embodiment is movable by the mirror moving means 25 in the optical axis direction of the seed light L2 immediately after being oscillated from the seed light oscillator 3, and as described later, Used to change the wavelength of light.

The second total reflection mirror 22 is fixed to be tilted at a predetermined angle with respect to the optical axis of the seed light L2 after being reflected by the first total reflection mirror 21. More specifically, when the left-right direction in FIG. 1 is 0°, the inclination angle of the second total reflection mirror 22 with respect to it is set to about 1 to 2°.
As a result, the seed light L2 reflected by the second total reflection mirror 22 enters the end surface 4A of the nonlinear optical crystal 4 in an inclined state, so that the pump light L1 and the seed light L2 are separated at the end surface 4A. are now intersecting.

The convex lens 23 focuses the seed light L2 oscillated from the seed light oscillator 3 and reflected by the first total reflection mirror 21 toward the second total reflection mirror 22, and further focuses the seed light L2 on the end face of the nonlinear optical crystal 4. The seed light L2 is made to enter the center of the light beam 4A obliquely so that the seed light L2 intersects with the pump light L1 at the end surface 4A.
That is, when the first total reflection mirror 21 is moved by the mirror moving means 25, the incident position of the seed light L2 with respect to the convex lens 23 is changed, but the focal position of the convex lens 23 is such that the condensed seed light L2 is After being reflected by the total reflection mirror 22, the light is set to be focused on the center of the end face 4A of the nonlinear optical crystal 4.
Here, when the seed light L2 guided by the light guiding means 5 does not intersect with the pump light L1 at the end surface 4A, for example when maintenance is performed on the terahertz light generating device 1, the nonlinear optical crystal 4 is The crystal is moved by the crystal moving means 14 so that the intersection position is located at the end face 4A.

In the terahertz light generating device 1 of this embodiment, it is possible to change the wavelength of the terahertz light TH depending on the type of the object O to be inspected, but to do so, the phase matching conditions for generating the terahertz light TH must be met. Things will change.
Therefore, the control means 6 changes the wavelength of the seed light L2 oscillated from the seed light oscillator 3, and controls the light guide means 5 to adjust the intersection angle θ between the pump light L1 and the seed light L2 to the above-mentioned phase. An operation is required to change the angle to a required angle that satisfies the matching condition.
Specifically, by moving the first total reflection mirror 21 along the optical path of the seed light L2 immediately after being oscillated from the seed light oscillator 3, the seed light L2 is made to enter the end surface 4A of the nonlinear optical crystal 4. The angle of incidence is changed, thereby changing the intersection angle θ between the pump light L1 and the seed light L2.
Since the position of the first total reflection mirror 21 is registered in the control means 6 for each wavelength of the terahertz light TH to be generated, by instructing the control means 6 which terahertz light TH to use, the position of the first total reflection mirror 21 is automatically set. 1. By moving the total reflection mirror 21, the intersection angle θ between the pump light L1 and the seed light L2 can be changed.
However, if there is a mechanical error in the mirror moving means 22 of the light guide means 5, the position of the first total reflection mirror 21 is shifted, and the seed light L2 enters the nonlinear optical crystal at an angle different from the predetermined incident angle. It will be incident on 4.
As a result, the intersection angle θ between the pump light L1 and the seed light L2 does not satisfy the phase matching condition, and the required terahertz light TH cannot be obtained. After changing, it is necessary to check whether the pump light L1 and the seed light L2 are actually incident on the end face 4A of the nonlinear optical crystal 4 at the required intersection angle θ, and if an error is found. needs to fix this.

Therefore, the terahertz light generating device 1 of this embodiment is equipped with a crossing angle measuring device 31 that measures the crossing angle θ between the pump light L1 and the seed light L2 after being guided by the light guiding means 5. If the intersection angle θ is deviated as a result of this, it is possible to correct this.
The crossing angle measuring device 31 is provided between the light guide means 5 and the nonlinear optical crystal 4, and more specifically, on the optical axis of the pump light L1 irradiated by the pump light oscillator 2, Further, it is provided on the optical axis of the seed light L2 immediately after being reflected by the second total reflection mirror 22 of the light guiding means 5.
As shown in FIG. 2, the crossing angle measuring device 31 includes two half-wave plates 32A and 32B provided on the optical path of the pump light L1 and the seed light L2, and a half-wave plate 32A and a half-wave plate 32A. A polarizing beam splitter 33 provided between the wavelength plate 32B, an iris plate 34 as an intersection position defining member provided on the optical path of the pump light L1 and the seed light L2 extracted by the polarizing beam splitter 33, An iris plate moving means 35 for moving the plate 34, a camera 36 as an imaging means for receiving the pump light L1 and seed light L2 that have passed through the pores 34a as a passage portion formed in the iris plate 34, and the iris plate. 34 and an inter-member distance measuring means 37 for measuring the inter-member distance D between the camera 36 and the camera 36.
The control means 6 also includes an inter-optical axis distance measuring means 38 for measuring an inter-optical axis distance d between the optical axis of the pump light L1 and the optical axis of the seed light L2 from the image taken by the camera 36; Calculating means 39 is provided for calculating an intersection angle θ between the pump light L1 and the seed light L2 from the inter-axial distance d and the inter-member distance D.

The 1/2 wavelength plates 32A and 32B are conventionally known optical elements that adjust the polarization direction of passing light.
Of the two 1/2 wavelength plates 32A and 32B, the 1/2 wavelength plate 32A located on the side of the pump light oscillator 2 and the light guiding means 5 transmits the pump light L1 and seed light L2 transmitted to the polarizing beam splitter 33. This is used to adjust the rate of reflection.
In this embodiment, the reflectance is set such that, for example, 5 to 10% of the pump light L1 and seed light L2 that have reached the polarizing beam splitter 33 are reflected toward the camera 36 side.
On the other hand, the half-wave plate 32B located on the side of the nonlinear optical crystal 4 allows the polarization direction of the pump light L1 and the seed light L2 that have passed through the polarization beam splitter 33 without being reflected to be incident on the nonlinear optical crystal 4. The polarization direction is then returned to the original polarization direction.

The polarizing beam splitter 33 is a conventionally known optical element that reflects light in a predetermined polarization direction and transmits light in other polarization directions. The adjusted pump light L1 and seed light L2 are reflected toward the camera 36 (lower in the figure).
In this embodiment, a reflective surface is provided at an angle of 45° to the optical axis of the pump light L1 emitted from the pump light oscillator 2, and therefore the pump light L1 is rotated at an angle of 90° by the polarizing beam splitter 33. It is designed to reflect at different angles.
On the other hand, after the seed light L2 is also reflected by the polarizing beam splitter 33, it intersects with the pump light L1 on the camera 36 side.
Here, the intersection angle θ between the pump light L1 reflected by the polarizing beam splitter 33 and the seed light L2 and the intersection angle θ between the pump light L1 and the seed light L2 transmitted through the polarizing beam splitter 33 are the same angle. .
Further, the intersection position of the pump light L1 reflected by the polarization beam splitter 33 and the seed light L2 and the intersection position of the pump light L1 and the seed light L2 transmitted through the polarization beam splitter 33 are the same as those of the pump light oscillator 2 and the seed light L2. The optical path length from the oscillator 3 becomes the same.

The iris plate 34 is formed of a plate-like member having a thickness of 0.2 to 0.3 mm, for example, and is provided so as to be perpendicular to the optical axis of the pump light L1. The above-mentioned pore 34a is provided as a passage section approximately in the center of the iris plate 34, and the pore 34a is provided in alignment with the optical axis of the pump light L1.
The iris plate moving means 35 moves the iris plate 34 in the optical axis direction of the pump light L1, and may adopt a mechanism in which the iris plate 34 is moved using, for example, a ball screw rotated by a driving means. .

Next, the pore 34a of the iris plate 34 is formed in a circular shape with a diameter of about 0.5 mm, and the pump light L1 and seed light L2 reflected by the polarizing beam splitter 33 pass through the iris plate 34. When incident, the cross-sectional shape is an ellipse with a length of about 2 to 3 mm and a width of about 5 to 6 mm.
Therefore, even if the iris plate 34 is located at the intersection of the pump light L1 and the seed light L2, and the pump light L1 and the seed light L2 pass through the pore 34a, only the portion near the optical axis of these light passes. , other parts will be blocked.
As a result, the pump light L1 and the seed light L2 are received by the camera 36 in a state where the cross-sectional shape is eclipsed into a circular shape by the pores 34a (see FIG. 3).
In this way, in the iris plate 34 of this embodiment, only the high-energy parts of the pump light L1 and the seed light L2 are extracted through the pores 34a, and specifically, the diameter of the pores 34a is set as follows. It can be set as follows.
First, when the pump light L1 and the seed light L2 are so-called Gaussian beams, the beam intensity becomes high at the optical axis portion and decreases toward the outer periphery.
The first method is to connect two points centered on the optical axis of the laser beam, where the beam intensity is 1/e ² of the peak value (optical axis), and calculate the distance as the diameter of the pore 34a. One possible method is to do this.
A second method is a method in which when the beam intensity distribution of the laser beam is Gaussian distribution, the diameter of the pore 34a is set to a distance four times (D4σ) the standard deviation of the Gaussian curve that indicates the intensity distribution. is possible.

A conventionally known camera can be used as the camera 36, and when the photographed image is sent to the control means 6, it is converted into a gray scale using a conventionally known method, and the control means 6 pumps the brightness of each pixel. The positions of the optical axes of the light L1 and the seed light L2 are recognized.
Specifically, since the pump light L1 always passes vertically through the pore 34a of the iris plate 34, it is vertically incident on the same position of the light receiving element 36a of the camera 36.
For this reason, the control means 6 recognizes the position of the highest brightness among the lights received at the same position regarding the pump light L1 as the optical axis portion of the pump light L1 having a high beam intensity.
As described above, the optical path length of the pump light L1 and seed light L2 until they reach the iris plate 34 is the same as the optical path length of the pump light L1 and seed light L2 until they reach the end surface 4A of the nonlinear optical crystal 4. Therefore, the seed light L2 passes through the pore 34a of the iris plate 34 at the same angle of incidence as the angle of incidence on the end surface 4A.
The seed light L2 that has passed through the pore 34a is obliquely incident on the light receiving element 36a of the camera 36, and the control means 6 also controls the optical axis of the seed light L2 to adjust the position of the highest brightness to the light receiving element 36a of the camera 36. Recognize it as a part.

Here, if the intersection position of the pump light L1 and the seed light L2 shifts due to maintenance of the terahertz light generator 1, for example, the nonlinear optical crystal 4 is moved by the crystal moving means 14 to position the end face 4A. However, in conjunction with this, it is necessary to also move the iris plate 34 located at the same optical path length.
That is, if the iris plate 34 is not located at the intersection of the pump light L1 and the seed light L2, the light cannot pass through the pore 34a and will not be received by the light receiving element 36a.
Then, the control means 6 causes the iris plate moving means 35 to move the iris plate 34 in the optical axis direction of the pump light L1 at a pitch of, for example, 0.5 mm.
Then, a part of the seed light L2 comes to pass through the pore 34a, but if the optical axis portion of the seed light L2 does not pass through the pore 34a, the brightness of the light received by the light receiving element 36a decreases. Since the predetermined threshold value is not reached, the control means 6 recognizes that the optical axis portion of the seed light L2 does not pass through the pore 34a.
Then, when the iris plate 34 is located at the intersection of the pump light L1 and the seed light L2, the optical axis portion of the seed light L2 passes through the pore 34a, and the brightness of the received light in the light receiving element 36a increases as above. Since the threshold value is exceeded, the control means 6 can recognize the optical axis portion of the seed light L2.

When the control means 6 recognizes the optical axis of the pump light L1 and the optical axis of the seed light L2 in this way, the inter-optical axis distance measuring means 38 detects the position of the optical axis of the pump light L1 and the optical axis of the seed light L2. Measure the distance d between the optical axes and the position.
The inter-member distance measuring means 37 is constituted by a conventionally known linear scale, and the inter-member distance D between the iris plate 34 and the light receiving element 36a of the camera 36 located at the intersection of the pump light L1 and the seed light L2. Measure.
The calculation means 39 calculates the intersection of the pump light L1 and the seed light L2 from the distance d between optical axes measured by the distance measurement means 38 and the distance D between members measured by the distance measurement means 37. Calculate the angle θ.
In this embodiment, since the pump light L1 is perpendicularly incident on the light receiving element 36a, it is possible to easily calculate the intersection angle θ based on the distance d between the optical axes and the distance D between the members. (θ=atan(d/D)).
In this embodiment, the intersection angle θ between the pump light L1 and the seed light L2 calculated here means the incident angle of the seed light L2 with respect to the light receiving element 36a, and in other words, the end face 4A of the nonlinear optical crystal 4 This means the angle of incidence of the seed light L2 relative to the angle of incidence of the seed light L2.

Hereinafter, a procedure of adjustment work for generating terahertz light TH of a predetermined wavelength from the terahertz light generating device 1 using the crossing angle measuring device 31 having the above configuration will be described.
First, the control means 6 controls the wavelength of the seed light L2 corresponding to the predetermined terahertz light TH, and the wavelength of the seed light L2 in the light guiding means 5 for forming an intersection angle θ between the pump light L1 and the seed light L2 that satisfies the phase matching condition. 1. The position of total reflection mirror 21 is registered.
When the pump light oscillator 2 irradiates the pump light L1 and the seed light oscillator 3 irradiates the seed light L2, the pump light L1 enters the end face 4A of the nonlinear optical crystal 4, and the seed light L2 is transmitted to the light guiding means 5. After being guided, the light enters the end surface 4A at a required angle of inclination.
At this time, if the pump light L1 and the seed light L2 are incident on the end surface 4A of the nonlinear optical crystal 4 at an intersection angle θ that satisfies a predetermined phase matching condition, the required terahertz light TH is generated from the nonlinear optical crystal 4. becomes.
However, if the position of the first total reflection mirror 21 of the light guiding means 5 is slightly shifted due to mechanical error or the like, the seed light L2 does not enter the end surface 4A of the nonlinear optical crystal 4 at a predetermined incident angle. In this case, the required terahertz light TH cannot be obtained because the phase matching condition is not satisfied.

Therefore, in this embodiment, the pump light L1 and the seed light L2 are made incident on the intersection angle measuring device 31 provided between the light guide means 5 and the nonlinear optical crystal 4, and the pump light L1 and the seed light L2 are The intersection angle θ is measured and errors are corrected as necessary.
First, the pump light L1 emitted from the pump light oscillator 2 and the seed light L2 emitted from the seed light oscillator 3 and guided by the light guiding means 5 are 1/2 of the intersection angle measuring device 31. It passes through the wave plate 32A.
As a result, the polarization directions of the pump light L1 and seed light L2 are converted, and some of the pump light L1 and seed light L2 are reflected by the polarizing beam splitter 33, and the others pass through the downstream half-wave plate 32B. After that, it enters the nonlinear optical crystal 4.

The pump light L1 and seed light L2 reflected by the polarizing beam splitter 33 then enter the iris plate 34, and at this time the iris plate 34 is positioned at the intersection of the pump light L1 and the seed light L2. .
As a result, the optical axis portions of the pump light L1 and the seed light L2 pass through the pores 34a of the iris plate 34, and the pump light L1 and the seed light L2 are received by the camera 36.
Then, the inter-optical axis distance measuring means 38 of the control means 6 measures the inter-optical axis distance d between the optical axis of the pump light L1 and the optical axis of the seed light L2, while the inter-member distance measuring means 37 measures the inter-optical axis distance d between the optical axis of the pump light L1 and the optical axis of the seed light L2. The distance D between the members and the light receiving element 36a of the camera 36 is measured.
When the distance d between optical axes and the distance D between members are measured in this way, the calculation means 39 calculates the intersection angle θ between the pump light L1 and the seed light L2 from these measurement results.

When the calculation means 39 calculates the intersection angle θ between the pump light L1 and the seed light L2 in this way, the control means 6 determines whether the calculated intersection angle θ satisfies the phase matching condition necessary for irradiating the terahertz light TH. Determine whether or not the
When the crossing angle θ does not satisfy the phase matching condition, the control means 6 moves the first total reflection mirror 21 by the mirror moving means 22 of the light guiding means 5, and corrects the optical path of the seed light L2. The crossing angle θ between the light L1 and the seed light L2 is corrected, and the above-described operations are repeated until the crossing angle θ satisfies the phase matching condition.

As described above, according to the terahertz light generating device 1 of this embodiment, by using the crossing angle measuring device 31, the crossing angle θ between the pump light L1 and the seed light L2 can be easily measured. It is possible to easily match the above-mentioned crossing angle θ to the phase matching condition.
On the other hand, the conventional terahertz light generating device 1 does not include the crossing angle measuring device 31, which makes the task of matching the crossing angle θ between the pump light L1 and the seed light L2 with the required phase matching angle complicated. Ta.
To explain specifically using the configuration of FIG. 1, conventionally, in order to measure the intersection angle θ between the pump light L1 and the seed light L2, the nonlinear optical crystal 4 is removed from the optical path and a camera is installed on the optical path. do.
Subsequently, while measuring the position of the camera with respect to the intersection position of the pump light L1 and the seed light L2, the distance d between the optical axes of the pump light L1 and the seed light L2 photographed by the camera is measured multiple times, The intersection angle θ between the pump light L1 and the seed light L2 was calculated from the distance from this intersection position to the camera and the distance d between optical axes at each measurement position.
However, this method requires the work of removing and attaching the nonlinear optical crystal 4, which is not only very complicated, but also causes the position of the nonlinear optical crystal 4 to shift during the work.
In this embodiment, since there is no need to remove the nonlinear optical crystal 4, the work is not complicated, and no mechanical deviation occurs due to the work, so the intersection angle θ between the pump light L1 and the seed light L2 is can be easily measured, and it is also possible to prevent deviations from occurring when correcting the intersection angle θ.

In the above embodiment, the pump light oscillator 2 and the seed light oscillator 3 are arranged so that the pump light L1 and the seed light L2 immediately after oscillation are parallel to each other. The angle at which the light is incident on the reflection mirror 21 may be changed as appropriate. In this case, the angles at which the first total reflection mirror 21 and the second total reflection mirror 22 are supported may be adjusted so as to satisfy the phase matching condition.
Further, in the above embodiment, the light guiding means 5 is adapted to guide the seed light L2, but it may also guide the pump light L1, or may be configured to guide the pump light L1 and the seed light L2. Good too. For example, it is also possible to apply the configuration shown in FIG. 2 in Patent Document 1 mentioned above.
Further, the first total reflection mirror 21 does not necessarily need to be moved completely along the optical axis (optical path) of the seed light L2 immediately after being oscillated from the seed light oscillator 3.
In other words, if the reflection angle of the first total reflection mirror 21 with respect to the seed light L2 is the same, even if the first total reflection mirror 21 is moved along a path that is inclined with respect to the optical axis (optical path) of the seed light L2. good. In this case, when the first total reflection mirror 21 moves along the inclined path, the position where the seed light L2 is incident will shift.
Furthermore, although the iris plate 34 is moved using the iris plate moving means 35 controlled by the control means 6, a moving means for manually moving the iris plate 34 may also be used.

1 Terahertz light generator 2 Pump light oscillator 3 Seed light oscillator 4 Nonlinear optical crystal 5 Light guide means 6 Control means 21 First total reflection mirror 22 Second total reflection mirror 23 Convex lens 25 Mirror moving means 31 Intersection angle θ measuring device 33 Polarization Beam splitter (extraction means)
34 Iris plate (intersection position regulating member)
34a Pore (passing part) 35 Iris plate moving means 36 Camera (imaging means) 37 Inter-member distance measuring means 38 Inter-optical axis distance measuring means 39 Calculating means L1 Pump light L2 Seed light TH Terahertz light

Claims (4)

A pump light oscillator that oscillates pump light, a seed light oscillator that oscillates seed light, and a nonlinear optical crystal that generates terahertz light when the pump light and the seed light are incident at an intersection angle that satisfies a required phase matching condition. , a light guiding means for guiding at least one of the pump light and the seed light so that the pump light and the seed light are incident on the nonlinear optical crystal at an intersection angle that satisfies the required phase matching condition; In a terahertz light generation device equipped with
an extraction means provided between the light guiding means and the nonlinear optical crystal , for taking out a part of the pump light and the seed light and irradiating the rest onto the nonlinear optical crystal; and a pump taken out from the extraction means. an intersection position defining member provided at an intersection position of the light and the seed light , and having a passage section formed therein for passing the pump light and the seed light ; an imaging means for receiving light, an optical axis distance measuring means for measuring an optical axis distance between the pump light and the seed light based on an image received by the imaging means, and a distance between the optical axes and the imaging means. A terahertz light generation device characterized by comprising: calculation means for calculating an intersection angle between the pump light and the seed light from the distance between the members to the intersection position defining member. The light guide means calculates the cross angle between the pump light and the seed light based on the calculation result of the cross angle between the pump light and the seed light by the calculation means so that the cross angle between the pump light and the seed light satisfies the phase matching condition . The terahertz light generation device according to claim 1, wherein a light guide path of the pump light or the seed light is changed. comprising a moving means for moving the intersection position defining member along the optical axis of either the pump light or the seed light ;
determination means for determining whether or not the intersection position defining member is located at the intersection position of the pump light and the seed light , based on an image of the pump light and the seed light received by the imaging means; Prepare,
If the determining means determines that the crossing position defining member is not located at the crossing position of the pump light and the seed light , the moving means moves the crossing position determining member between the pump light and the seed light. 3. The terahertz light generating device according to claim 1, wherein the terahertz light generating device is moved to the intersection position . A pump light oscillator that oscillates pump light, a seed light oscillator that oscillates seed light, and a nonlinear optical crystal that generates terahertz light when the pump light and the seed light are incident at an intersection angle that satisfies a required phase matching condition. , a light guiding means for guiding at least one of the pump light and the seed light so that the pump light and the seed light are incident on the nonlinear optical crystal at an intersection angle that satisfies the required phase matching condition; For a terahertz light generator equipped with
Taking out a part of the pump light and the seed light before entering the nonlinear optical crystal,
disposing an intersection position defining member having a passage portion through which the pump light and the seed light can pass, at an intersection position where the extracted pump light and the seed light intersect;
receiving the pump light and the seed light that have passed through the passage portion of the intersection position defining member by an imaging means;
The distance between the pump light and the seed light is determined from the distance between the optical axes of the pump light and the seed light recognized from the image taken by the imaging means and the distance between the members from the imaging means to the intersection position defining member. A terahertz light generation method characterized by calculating an intersection angle.

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